An ultrasonic diagnostic equipment is an equipment for observing an internal state of an examination object by transmitting an ultrasonic wave from an ultrasonic probe (probe) arraying ultrasonic transducer elements into the examination object, receiving at the ultrasonic probe the ultrasonic wave returned after being reflected inside the examination object, and signal-processing and imaging the received ultrasonic wave. As an ultrasonic beam control method in the ultrasonic diagnostic equipment, there are sector scanning method and linear scanning method. The sector scanning method is a scanning method, wherein a measurement cross sectional layer is expressed as polar coordinates, a wave transmitting position of an ultrasonic wave is set to an origin, a traveling direction of the ultrasonic wave is designated as a diameter direction, and a wave transmitting direction is designated as an angle direction. The linear scanning method is a scanning method, wherein a measurement cross sectional layer is expressed as Cartesian coordinates, a traveling direction of an ultrasonic wave is designated as one axis, and a wave transmitting position of the ultrasonic wave is moved on the other orthogonal axis.
In an ultrasonic diagnostic equipment for performing the linear scanning by using arrayed transducer elements of an ultrasonic probe, focusing technique, in which convergence of ultrasonic beam is performed by using the plurality of arrayed transducer elements concurrently is utilized. There is transmission focusing technique, wherein control is made so that ultrasonic beam is converged at a certain test part in the body by shifting generation start timing of pulse given to respective transducer elements of an ultrasonic probe. Further, there is an ultrasonic diagnostic equipment for performing synthetic aperture scanning.
Descriptions will be hereinafter given of the focusing technique briefly. A transmission timing signal is output from a transmission timing control circuit to a driver at a timing that ultrasonic beam concurrently reaches the part where the ultrasonic beam is desired to be converged. The driver generates ultrasonic transmission pulse according to the transmission timing signal, and transmits the ultrasonic transmission pulse to a transducer element. Each driver and each transducer element are connected one for one. A signal converted to an ultrasonic wave at the transducer element is reflected inside the examination object, converted to an electrical signal at the transducer element, and delay-added at a reception beam forming device.
In the synthetic aperture scanning, drive pulse is generated in a transmission circuit, and a selected transducer element is driven. The transducer element generates ultrasonic pulse, and ultrasonic pulse reflected inside the examination object is received at the transducer element as an echo ultrasonic wave. The receiver signal is amplified, converted to digital data, and written in a memory. After writing in the memory is finished, a different transducer element is selected, and a receiver signal is written in the memory as above. The respective receiver signals stored in the memory are added with a given time difference. The added receiver signals are signal-processed at a signal processor, and shown on a display part. When the examination object remains stationary during reception, a signal from a specific inner part of the examination object can be emphasized, and sharp reception directivity can be obtained. Some examples of conventional ultrasonic diagnostic equipments will be hereinafter cited.
“Ultrasonic diagnostic equipment” disclosed in Japanese Unexamined Patent Application Publication No. H07-67879 is an ultrasonic diagnostic equipment for performing the synthetic aperture, wherein image deterioration caused by motion of an examination object is prevented. Arrayed transducer elements are driven by a transmission circuit, and ultrasonic waves are transmitted into an examination object. Among echoes respectfully received by the transducer elements, one or more signals from one or more given transducer elements is/are selected by switches. The signal is appropriately amplified at an amplifier, converted to a digital signal at an A/D converter, and then delay-added at a beam synthetic part, and stored in a memory. As above, an ultrasonic wave is transmitted again, and a signal of other transducer element is selected by a switch. Similar signal processing is performed at the amplifier, the A/D converter, and the beam synthetic part, and then the signal is added to the delay-added signal which has been stored in the memory. These added signals are provided with signal processing at a signal processing part, and then shown on a display part.
“Ultrasonic diagnostic equipment” disclosed in Japanese Unexamined Patent Application Publication No. 2000-152937 is an ultrasonic diagnostic equipment, wherein the number of transmission drivers is reduced without losing a shape of reception beam. By inserting a switch (diode) between the transmission driver and a transducer element, a plurality of transducer elements can be driven by one driver. In reception, signals of the respective transducer elements can be processed independently.
A concrete example of the conventional ultrasonic diagnostic equipment which performs the linear scanning will be hereinafter described with reference to FIG. 13. FIG. 13 is a block diagram of a front end part of the ultrasonic diagnostic equipment. In FIG. 13, a probe 1 is an ultrasonic probe comprising an array of transducer elements 2-1 to 2-32. The transducer elements 2-1 to 2-32 are actuators/sensors for transmitting and receiving ultrasonic waves. High voltage switches 3-1 to 3-32 are switches for selecting transducer elements corresponding to an aperture to be used, and applying high voltage transmission pulse. Pulsers 4-1 to 4-16 are transmission drive circuits generating transmission pulse. A trigger generator 5 is a means for generating transmission trigger signals. Limiters 6-1 to 6-16 are means for clipping the high voltage transmission pulse to protect subsequent stage circuits. A cross point switch (CPS) 7 is a means for sorting and adding limiter outputs. A/D converters 8-1 to 8-8 are means for converting analog receiver signals to digital signals. A beam forming device 9 is a means for delay-adding the digital converted data. A controller 10 is a means for performing timing control of a transmission circuit and a reception circuit.
Operation of the conventional ultrasonic diagnostic equipment constructed as above will be hereinafter described. The trigger generator 5 generates a transmission trigger signal, a timing signal for outputting ultrasonic pulse. According to the transmission trigger signal, the pulsers 4-1 to 4-16 generate transmission pulse. In order to protect circuits such as the subsequent stage cross point switch from high voltage transmission pulse generated at the pulsers 4-1 to 4-16, the limiters 6-1 to 6-16 clip the high voltage transmission pulse to enter the cross point switch 7. By selectively turning ON/OFF the high voltage switches 3-1 to 3-32, the high voltage transmission pulse is applied to only transducer elements to be driven. By this selective operation, a position and a width of an aperture of the probe 1 are determined. Selected 16 transducer elements of the probe 1 transmit ultrasonic waves to the examination object.
Reflected ultrasonic waves from the examination object are received at the transducer elements 2-1 to 2-32. The receiver signals pass selected 16 high voltage switches, enter the cross point switch 7 via the limiters 6-1 to 6-16. At the cross point switch 7, the receiver signals are sorted and added, and then changed into eight synthetic receiver signals. The synthetic receiver signals are converted to digital signals at the A/D converters 8-1 to 8-8. The digital converted receiver signals are delay-added and directivity is adjusted at the beam forming device 9. The resultant output signal is converted to an image signal at an unshown circuit, and displayed. The controller 10 performs timing control of the transmission circuit and the reception circuit of the ultrasonic waves.
In the foregoing conventional ultrasonic diagnostic devices, however, many circuits are required, and therefore, there is a problem that manufacturing the conventional ultrasonic diagnostic device is costly. In particular, there is a problem that manufacturing the transmission drive circuit (pulser) for generating transmission pulse is significantly costly.